Lake and Marine Environments

A steady increase in dissolved organic matter (DOM) has been observed in several lakes in Japan, even though extensive measures have been implemented in order to reduce organic pollutant loadings from their catchment areas. For instance, in Lake Biwa, the largest lake in Japan, the concentration of DOM has been gradually increasing in the surface water since 1984. It is likely that some recalcitrant DOM has been accumulating in the water of Lake Biwa. This phenomenon is new and was not given any previous consideration. The accumulation of recalcitrant DOM in lake water certainly influences the way in which the protection of lake environments should be managed, because (1) recalcitrant DOM can be a major precursor to carcinogenic trihalomethanes produced during chlorination in water treatment plants, and (2) DOM is regarded as an influence on the biological activity of phytoplankton and bacteria. NIES has developed a method by which DOM is separated into well-characterized macro-fractions, in order to examine the physical-chemical characteristics, dynamics, and origin of DOM in Lake Kasumigaura (second largest lake in Japan), and to evaluate the effects of DOM on the growth and species composition of phytoplankton in the lake and on the quality of the lake water for use as drinking water. Our research findings suggest that effluent from sewage treatment plants may contribute substantially to the recalcitrant DOM in the lake water, even though most of the recalcitrant DOM is still attributable to river inflows and autochthonous sources.

Seasonal variations in dissolved organic matter (DOM), aquatic humic substances (AHS), and hydrophilic acids (HIA) and recalcitrant DOM, AHS, and HIA at the center of Lake Kasumigaura (1997). Recalcitrant fractions were defined as those remaining after a 100-day aerobic incubation.


In coastal regions like Japan's Seto Inland Sea, problems such as eutrophication and anomalous algae blooms such as red tides occur as a result of excess phosphorus and nitrogen and lack of silicon caused by anthropogenic effects. It is important to take measurements at frequent intervals because a large number of factors are involved (such as weather condition, vertical mixing, amount of sunlight, inflow from rivers, etc.). For monitoring the atmospheric factors, continuous measurement and data display systems such as AMeDAS already exist. However, it has been more difficult to monitor marine factors. Since 1991, NIES has been owing much to the cooperation of a shipping company, which allowed the installation on its ferries, the Sunflower-Ivory and its predecessors, of equipment for daily monitoring of parameters such as nutrients, water temperature, salinity, and chlorophyll concentrations (an indicator of the concentration of phytoplankton). In addition , we are developing technology to allow continuous monitoring by receiving the data at NIES via satellite telephone. In the future NIES may further seek to develop this work using a larger network of ferries. If this can be achieved, data from many locations will be available, making it possible to better predict changes of marine environmental conditions and to improve the potential for water quality management in coastal zones.

Seawater monitoring and online data transmission systems installed on board the ferry Sunflower-Ivory. It takes continuous measurements of seawater temperatures, salinity, phytoplankton concentrations, etc.

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